advantages and disadvantages of simple digital clock

digital clock using 8051 advantages and disadvantages

Digital clock displays the time using numbers. This circuit is used in many applications like cars, railway stations, houses, offices, etc. in order to provide accurate time and date. In this type of applications, normally we use RTC (Real Time Clock) ICs to display the time and date accurately. This circuit displays the time on LCD. For this clock, we can set the time at any instant. Here the clock works in 24 hour mode and the RTC chip is configured by programming 8051 controller.

Circuit Principle:

Here 8051 controller continuously reads the data from Real time clock and process it in correct order to display the time on LCD. INT1 of the 8051 controller is used to set the time to the digital clock. If you make P3.3 pin LOW then interrupt arises and set_time function is called to set the time. To set the time to the clock use P1.4 and P1.5 pins. P1.4 is used to vary the hours and P1.5 is used to vary the minutes. After setting the time make P1.6 high to run the clock with the time set by user.

Circuit Components:

8051 microcontroller
Project PCB
Programming cable
DC Battery or 12V, 1A adaptor
DS12C887 RTC IC
16*2 alphanumeric LCD
Push buttons – 4
Slide switches – 3
2 ceramic capacitors – 33pF
12 MHz crystal
Electrolytic capacitor – 10uF, 16V
Resistor (1/4 watt) – 10k
Pot – 10k
5V DC power supply circuit
Single pin connecting wires
Circuit Design:

The circuit shows you how interface RTC IC to the 8051 controller. Port P0 is used as a data port of Real time clock. Port P2 of controller is connected to the data pins of LCD. Pins P1.1, P1.2 and P1.3 of controller are connected to the RS, RW, EN pins respectively. P1.0 is connected to the RESET of RTC. Push buttons are connected to the P1.4 and P1.5. These are used set the time. P1.6 is configured as START pin used to run the clock with time set by the user. P3.3 is connected to the push button used to call the set_time function.

DS12C887 Real Time Clock:

This IC is used most of the applications to provide accurate time and date. This IC provides the time in both 12 hour mode and 24 hour mode. This IC also provides calendar components day, month and year. This RTC uses internal lithium battery to keep the time and date updated when power is failed. This IC has 128 bytes of RAM memory. In these 128 bytes of RAM 14 bytes are used for time, date and registers. Remaining 114 bytes are used to store general purpose data.

The control registers of RTC are accessible only when the power is applied from external source. This IC requires more than 4.25V power supply and the control registers are accessible after 200ms when external power is supplied.

Pin Description:

MOT: It is a bus type selection pin used to select between Intel and Motorolabus types. This pin is connected to VCC to select Motorola bus type and connected to GND or unconnected to select Intel bus type.
2, 3: Unused pins
4 – 11 (AD0 – AD7): These pins are bidirectional address and data lines of RTC. On these pins address is present in the first portion of cycle and data is present in the second portion of bus cycle.
12 (GND): This pin is connected to Ground.
13 (CS): This pin must be low to access the chip during read and write operations.
14 (AS): The high pulse on this pin is used to demultiplex the data and address.
15 (R/W): This pin is used for read or writes operations.
16: Unused pin
17 (DS): This is a Data Strobe pin.
18 (RESET): The low pulse on this pin resets all the flags and interrupts but it does not affects time and date.
19 (IRQ): Thisis active low pin used as an interrupt input to the controller.
20 – 22: Unused pins
23 (SQW): Used to generate square wave with predefined frequencies
24 (VCC): This pin is connected 5V supply